The use of the reverse breakdown characteristic of a zener diode as a reference voltage is known in the art. Normally, the zener diode is connected in series with an impedance across a source of operating potential with the zener voltage serving as a source of reference voltage. Ideally, the zener voltage should be absolutely constant as a function of temperature variations and changes in the operating voltage. However, due to the finite ynamic resistance of the zener diode, the zener voltage (V.sub.Z) produced by a zener diode changes (e.g., increases) when the current through the zener diode changes (e.g. increases) due to a change (e.g. increase) in the operating voltage. Furthermore, a zener diode typically has a (positive or negative) temperature coefficient, whereby its zener voltage varies as a function of temperature. An additional problem is that a zener diode having a desirable temperature coefficient may not have the exact value of the voltage desired. For example, a zener diode having desirable characteristics and a low positive temperature coefficient is a P+N+ diode whose zener voltage is approximate 5.6 volts. However, in many applications, it is desirable and/or necessary to have a reference voltage other than 5.6 volts. It is therefore necessary to process and alter the zener voltage to produce the desired reference voltage. It is further necessary that the desired reference voltage so produced be relatively constant over a wide range of temperature and operating voltage and variations related to semiconductor process changes.